What happens to the beam as distance from the transducer increases?

• A. Becomes more uniform
• B. Becomes more divergent
• C. Increases in frequency
• D. More absorbed by tissue

Answer: (A)

As the ultrasound beam travels, its initial near-field pattern is shaped by the interference of many small wavefronts, which creates a nonuniform intensity with bright and dark regions. As distance increases, those interference effects average out in the far field, so the cross-sectional energy distribution becomes smoother and more even. The frequency of the beam is fixed by the transducer and does not increase with distance, and while the beam does spread (diverge) as it travels, the overall cross-sectional intensity tends to become more uniform rather than simply more divergent. Attenuation by tissue does rise with distance, but that describes energy loss, not the beam’s uniformity pattern.